maybe you can try "dark pool trade" on lakebtc or bitfinex.
I don't think these exist as the bitcoin market is not large enough for these types of trades. I agree with mobius above that you should look to second market if you have the capital to trade ~25 BTC at a time at least. These trades would not directly hit the exchange and you would be dealing with a trusted party (IMO).
Hit the market! and you can profit from it, it's the goal of trading.
To the moon will be true.